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Vertical Alignment Optimization

Updated October 19, 2017

This article applies to:
  • Softree Optimal

Alignment design is a fundamental part of any corridor engineering project. The alignment position directly affects the cost of the project. Softree Optimal can be used to create new designs or refine and verify existing designs.

Three-dimensional alignment design is a complicated geometric problem. In addition to standards such as design speed curvatures and maximum grade, engineers must contend with a variety of conditions and restrictions such as right of way, utilities and crossing grades. These constraints often make the alignment problem even more challenging.

Softree Optimal can quickly calculate the earthwork cost of any alignment (see previous exercises); in mathematical optimization terminology, this is called the cost function. To optimize a vertical alignment, Softree Optimal minimizes the cost function over all possible alignments. Your job as an engineer/designer is to constrain Softree Optimal to reasonable alignments.

Vertical alignment optimization is based on the following parameters and constraints:

  • Earthwork Costs - Excavation, embankment and haul costs (see previous section).

  • Pit Locations - Waste and borrow locations and associated costs (see previous section).

  • Design Standards - Maximum curvature (minimum K values), minimum and maximum grades.

  • Control Points - elevation and grade constraints:

    • Terminating Conditions - Starting and ending elevations and grades.

    • Control Points - Defined station, elevation points (intersections, driveways, etc.).

  • Special Constraints:

    • Cut or fill depth constraints – for example minimum fill requirements in wet areas.

    • Preferred direction for earth movement.

    • Full Bench Cut requirement.

Softree Optimal allows you to create multiple vertical alignments in one document. This lets you to try different constraints and scenarios. To work with and compare multiple horizontal alignments, it is necessary to create multiple documents (DSN files); in this event, it is sometimes convenient to open two instances of the Location module.

An optimal vertical alignment is based on all the current design settings, e.g. horizontal alignment, sub-surface layers, template assignments, ground types, etc.

Note (for those familiar with RoadEng®): Vertical optimization is not recommended if you have fixed sections defined. A change in vertical position may produce unwanted results on a fixed section. Fixing sections (if desired) can be done later once both the horizontal and vertical alignments are finalized.